Sometime in 1949, the change was made by riveting the post to the magazine. I have a spare magazine(1954) that I ground off the rivet to remove the post. You can see that the magazine was predrilled and post was fabricated to fit the hole and then peened.
(https://i.ibb.co/NCHkhFP/IMG-2310.jpg) (https://ibb.co/mTMYsRw)
(https://i.ibb.co/fMFP6CF/IMG-2210.jpg) (https://ibb.co/rk018Z0)
(https://i.ibb.co/Z2h34Cp/IMG-2140.jpg) (https://ibb.co/KK9Y4Hp)
Before looking at my 1949, I had thought that the spring was loose fitting and that the reason for the rivet change was to hold it in place. But then I saw that there was a post holding the spring in place. Pictured is my ЮE 1217 SKS
(https://i.ibb.co/GRF34G1/IMG-2078.jpg) (https://ibb.co/KWmzpBQ)
Once I removed the pin holding magazine together I could see that the post was welded to magazine. Pictured is my ЮE 416 SKS.
(https://i.ibb.co/tY7G43P/IMG-2096.jpg) (https://ibb.co/TPVfkrq)
When I cropped some pictures, I noticed why the change was made to a rivet. Poor welding and weld was cracking.
(https://i.ibb.co/vhSNv8C/IMG-2170.jpg) (https://imgbb.com/)
(https://i.ibb.co/3s9kmDh/image.jpg) (https://imgbb.com/)
I added the top picture tonight. It looked a little odd, so I clicked on picture then on the + to enlarge. I then scrolled down to where the post is. It appears that the heat from the inside weld made a circular impression on the outside of magazine.